1. Field of the Invention
The present invention relates to an intake air control apparatus for a vehicular internal combustion engine in which a quantity of intake air provided to the engine is controlled using a variable control mechanism configured to control a valve opening characteristic of one or more intake valves, the valve opening characteristic including a combination of the valve lift and the valve opening phase angle. More particularly, the present invention relates to intake air quantity control of the internal combustion engine in a transient period between a low-load operating condition and a reacceleration operating condition of the engine and vehicle.
2. Description of the Related Art
In an internal combustion engine, generally an intake air quantity is controlled by adjusting an opening angle of a throttle valve installed within an intake air passage. As is well known in the art, this type of intake air flow quantity control can result in a large pumping loss at low and moderate engine operating loads when the opening angle of the throttle valve is particularly small. Attempts have been made in the prior art to control the intake air quantity independently of the throttle valve by varying the valve lift (i.e., the distance or amount of travel of the valve when fully opened) and/or the valve phase angle (i.e., the timing of opening and closing the valve relative to top dead center of the piston) of the intake valve.
Japanese Patent Provisional Publication No. 2002-256905 discloses an apparatus which includes a first variable valve operating mechanism for varying a valve lift (i.e., the distance or amount of travel) of an intake valve of an engine and a second variable valve operating mechanism for continuously varying a valve phase angle (i.e., the timing of opening and closing) of the intake valve. The apparatus is adapted to control an intake air quantity in the engine by controlling a valve opening characteristic of the intake valve which is determined based on the valve lift and the valve phase angle.
Japanese Patent Provisional Publication No. 2006-312943 discloses determining a limit value of a valve phase angle which may cause physical interference between the piston and the intake valve, for instance, by detecting an actual valve lift and by controlling a target value of the valve phase angle so as not to advance the valve phase angle beyond the limit value for the purpose of providing a large control region over which the valve lift and the valve phase angle can be controlled without causing the intake valve to contact the piston.